Aluminum alloy, and aluminum alloy casting

ABSTRACT

Provided are a metal alloy and more particularly, to an aluminum alloy used for electrical, electronic, and mechanical components, and an aluminum alloy casting manufactured using the aluminum alloy. The aluminum alloy according to an embodiment includes 4 to 13 wt % of silicon (Si), 1 to 5 wt % of copper (Cu), 26 wt % or more and less than 40 wt % of zinc (Zn), and a balance being aluminum (Al) and unavoidable impurities.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2010-0050693, filed on May 29, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a metal alloy, and more particularly,to an aluminum alloy used for electrical, electronic, and mechanicalcomponents, and an aluminum alloy casting manufactured using thealuminum alloy.

2. Description of the Related Art

Recently, the needs for high-strength materials that are more resistantto deformation are increasing as electronic products such as a notebookand a mobile phone become more complicated in aspects of appearances andfunctions. Particularly, components, such as a bracket supporting aportion of a liquid crystal display (LCD) panel and a hinge having thinand complicated shapes, require a lightweight material for a portabilityas well as a high strength similar to stainless steels (e.g., stainlesssteel 304). However, although stainless steels can be shaped by pressingor forging, the stainless steels have limitations in mass production andachievement of a precise product shape, and the stainless steels havinga specific gravity of about 8.00 g/cm³ are heavy. Therefore, the needfor developing a high-strength and lightweight alloy is increasing.

SUMMARY OF THE INVENTION

The present invention provides an aluminum alloy lighter than about ahalf of a weight of a typical stainless steel as well as having astrength similar to the typical stainless steel (e.g., stainless steel304) and better than a typical commercial aluminum alloy even through ageneral die casting method, and an aluminum alloy casting manufacturedusing the foregoing aluminum alloy. Objects of the present invention areexemplarily provided, and the scope of the present invention is notlimited by these objects.

According to an aspect of the present invention, there is provided analuminum alloy including: 4 wt % to 13 wt % of silicon (Si); 1 wt % to 5wt % of copper (Cu); 26 wt % or more and less than 40 wt % of zinc (Zn);and a balance being aluminum (Al) and unavoidable impurities.

According to another aspect of the aluminum alloy, a content of thesilicon (Si) may be 5 wt % to 10 wt %.

According to another aspect of the aluminum alloy, the content of thesilicon (Si) may be 5 wt % to 8 wt %. In this case, a content of thecopper (Cu) may be 2 wt % to 5 wt %, and further, a content of the zinc(Zn) may be 26 wt % to 35 wt %.

According to another aspect of the present invention, there is providedan aluminum alloy including: 4 wt % to 13 wt % of silicon (Si); 1 wt %to 5 wt % of copper (Cu); 26 wt % or more and less than 40 wt % of zinc(Zn); 0.1 wt % or less of strontium (Sr); and 43 wt % to 69 wt % ofaluminum (Al).

According to another aspect of the aluminum alloy, a content of thesilicon (Si) may be 5 wt % to 10 wt %.

According to another aspect of the aluminum alloy, the content of thesilicon (Si) may be 5 wt % to 8 wt %. At this time, a content of thecopper (Cu) may be 2 wt % to 5 wt %, and further, a content of the zinc(Zn) may be 26 wt % to 35 wt %.

According to another aspect of the aluminum alloy, a content of thestrontium (Sr) may be greater than 0 wt % and 0.04 wt % or less.

According to another aspect of the aluminum alloy, the content of thestrontium (Sr) may be greater than 0 wt % and 0.02 wt % or less.

According to another aspect of the aluminum alloy, the aluminum alloymay further include a total of 3 wt % or less (more than 0) of any oneor more elements selected from the group consisting of titanium (Ti),magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron (Fe), chromium(Cr), zirconium (Zr), scandium (Sc), and manganese (Mn).

According to another aspect of the present invention, there is providedan aluminum alloy casting which is manufactured by using the foregoingaluminum alloy

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 show tensile test results of a commercial ADC12 aluminum alloyand an aluminum alloy according to an embodiment of the presentinvention;

FIG. 2 shows a comparison result between microstructures of a commercialaluminum alloy and an aluminum alloy according to an embodiment of thepresent invention; and

FIGS. 3 and 4 show observation results on microstructures of an aluminumalloy according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will now be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. The invention may, however, be embodied inmany different forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art.

In embodiments of the present invention, a weight % (wt %) denotes aweight occupied by one component among a total weight of an alloy as apercentage. It can be understood that a boundary value is not includedwhen a range of weight % is more than or less than; and the boundaryvalue is included when simply designated as a range, or designated asequal to or greater than or equal to or smaller than.

In embodiments of the present invention, unavoidable impurities maydenote impurities which may be introduced unintentionally duringmanufacturing of an aluminum alloy or an aluminum casting.

An aluminum alloy according to an embodiment of the present inventionmay be formed by adding silicon (Si), copper (Cu) and zinc (Zn) to amain element, aluminum (Al). A content of aluminum, the main element ofthe aluminum alloy, may occupy the balance other than additionalelements. Therefore, the content of aluminum may be changed according tothe contents of the additional elements. The aluminum alloy may includeunavoidable impurities which are contained in each element itself orcontained unintentionally during an alloying operation.

For example, the aluminum alloy may contain 4 to 13 wt % of silicon, 1to 5 wt % of copper, and 26 wt % or more and less than 40 wt % of zinc,and a balance being aluminum and unavoidable impurities.

Silicon may be added to increase fluidity of a molten aluminum andimprove feeding ability during solidification. Also, in the case of analuminum-silicon alloy (Al—Si alloy), a hybrid structure having aprimary α-aluminum phase and a eutectic silicon phase may be formedduring casting. Mechanical strength may be considerably improved whenthe structure of the eutectic silicon phase is refined from a needleshape to a particulate shape or a fibrous shape by performing amodification treatment.

However, since mechanical properties are deteriorated in some cases dueto an increase in the brittleness of an alloy, products may be damagedwhen the products are separated from a mold during a die castingprocess. Therefore, when considering all the foregoing effects, siliconcontent according to the present embodiment may be limited to a range of4 to 13 wt %, specifically a range of 5 to 10 wt %, and morespecifically, a range of 5 to 8 wt % or less.

Copper has the maximum solubility of 5.6 wt % with respect to aluminumat a eutectic temperature of 548° C., and may exhibit a solid solutionstrengthening effect when dissolved in aluminum. Also, copper forms anAl—Zn—Cu compound by reacting with zinc and aluminum when coppertogether with zinc is added to aluminum. Since the Al—Zn—Cu compoundacts as obstacles preventing dislocation movements during thedeformation of an alloy or prevents grain growth, the compound maycontribute to improving the strength of the alloy.

However, when a copper content is too high, mechanical properties aredeteriorated due to an increase in brittleness. Also, since copper isheavier than aluminum, it is not effective to reduce the specificgravity of the alloy. Moreover, the excessive copper content may causecastability of aluminum to be deteriorated. Therefore, when consideringall the foregoing effects, the copper content in the present embodimentmay be limited to a range of 1 to 5 wt %, specifically, a range of 2 to5 wt %.

80 wt % of zinc is dissolved at 382° C. when added into aluminum, butthe solubility of zinc is rapidly decreased as temperature decreases.Therefore, in the case of the aluminum alloy according to the presentinvention, 18 wt % of zinc is dissolved in the matrix of the castaluminum alloy. At this time, undissolved surplus zinc may react withaluminum and copper to form the Al—Cu—Zn compound as described above.Therefore, it is necessary to add 26 wt % or more of zinc into aluminumin order to obtain both of the solid solution strengthening effect andcompound forming effect by means of zinc.

However, since zinc is an element heavier than aluminum, it isunfavorable to achieve a lightweight alloy. When a zinc content is morethan 38 wt %, strength may be decreased because a content of aneutectoid structure having low strength and high elongation may beincreased as the eutectoid transformation of a β-phase to a two-phasehybrid structure of β′-phase and α-phase is progressed. Also, since theeutectic Si-phase exists in the primary α-phase of the aluminum alloywhen the zinc content is 40 wt %, strength may be decreased due to anincrease in the grain size of the aluminum alloy. Therefore, the addedamount of zinc may be limited to less than 40 wt % in consideration ofthe foregoing effects.

An aluminum alloy according to another embodiment of the presentinvention may include 4 to 13 wt % of silicon (Si), 1 to 5 wt % ofcopper (Cu), 26 wt % or more and less than 40 wt % of zinc (Zn), 0.1 wt% or less of strontium (Sr) and 43 to 69 wt % of aluminum (Al).

For example, since strontium refines the crystal structure of analuminum alloy when strontium is additionally added, the strength of thealuminum alloy may be improved. That is, in the case of the aluminumalloy including silicon, the hybrid structure of the primary α-phase andeutectic Si-phase may be obtained during casting, and strontium maycontribute to improving strength by refining the structure of theeutectic Si-phase.

However, when strontium content is high, mechanical properties may bepoorer due to the crystallization of a compound including strontium.Therefore, when considering all these effects, the strontium contentaccording to the present embodiment may be limited to 0.1 wt % or less,specifically a range of greater than 0 wt % and 0.04 wt % or less, andmore specifically, a range of greater than 0 wt % and 0.02 wt % or less.

Also, a trace amount of additive elements in addition to silicon,copper, zinc and strontium may be added to aluminum, in order to improvethe strength of the aluminum alloy. The additive elements may includetitanium (Ti), magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron(Fe), chromium (Cr), zirconium (Zr), scandium (Sc), and manganese (Mn).The total amount of one or more elements selected from the aboveadditive elements may not exceed 3 wt %.

An aluminum alloy casting according to an embodiment of the presentinvention may be manufactured by using the above-described aluminumalloy. Herein, casting may include pure casting products manufacturedthrough casting and products obtained by molding a preformed castinginto predetermined shapes, e.g., a billet for extrusion, a plate forrolling, etc. Examples of the pure casting may include sand casting, diecasting, gravity casting, low-pressure casting, squeeze casting, lostwax casting, thixo casting, and the like.

Gravity casting may denote a method of pouring a molten alloy into amold by using gravity, and low-pressure casting may denote a method ofpouring a melt into a mold by applying a pressure to the surface of themolten alloy using a gas. Thixo casting, which is a casting processperformed in a semi-solid state, is a combination method of adopting theadvantages of typical casting and forging processes.

The aluminum alloy casting according to this embodiment may bemanufactured through any process including the foregoing processes, andmay have appropriate strength and machinability without performing aheat treatment. Alternatively, the aluminum alloy casting may besubjected to a heat treatment process after manufacturing according tothe applications and shapes thereof.

Hereinafter, Experimental Examples are provided to more clearlyunderstand the present invention. However, Experimental Examples beloware merely provided to more clearly understand the present invention,not to limit the scope of the present invention.

Table 1 shows alloy compositions of Experimental Examples according tothe present invention and Comparative Example, and results of tensilestrength as a mechanical property according to the alloy compositions.

TABLE 1 Tensile Strength Si Cu Zn Al Sr (MPa) Example 1 5.0 2.0 26.066.7 0.0 433.4 Example 2 6.0 2.0 26.0 65.7 0.0 441.6 Example 3 6.0 3.530.0 60.2 0.0 451.8 Example 4 6.0 5.0 30.0 58.7 0.0 439.4 Example 5 7.02.0 26.0 64.7 0.0 444.6 Example 6 7.0 2.0 30.0 60.7 0.0 440.9 Example 76.0 5.0 30.0 58.7 0.0 436.2 Example 8 6.0 3.5 31.0 59.2 0.0 443.1Example 9 6.0 2.0 32.0 59.7 0.0 419.7 Example 10 6.0 2.0 32.0 59.7 0.0416.8 Example 11 6.0 2.0 35.0 56.7 0.0 443.2 Example 12 6.0 3.5 35.055.2 0.0 444.0 Example 13 6.0 5.0 35.0 53.7 0.0 440.6 Example 14 8.0 2.026.0 63.7 0.0 441.7 Example 15 8.0 2.0 27.0 62.4 0.0 441.9 Example 168.0 3.5 28.0 60.2 0.0 436.7 Example 17 8.0 2.0 30.0 59.7 0.0 430.2Example 18 6.0 2.0 30.0 61.5 0.0 420.2 Example 19 6.0 2.0 30.0 61.7 0.02488.8 Example 20 6.0 2.0 28.0 63.6 0.02 465.1 Example 21 6.0 2.0 30.061.6 0.1 438.0 Comparative 0.0 2.1 30.1 67.4 0.0 321.1 Example 1

High purity aluminum (99.8%) and zinc (99.9%) were used in order tomanufacture the aluminum alloys according to the present invention, andaluminum master alloys, in which silicon, copper and strontium areadded, were used in order to add silicon, copper and strontium,respectively.

Each alloying element was melted by using an electric resistancefurnace, and degassing and ash removing were performed prior to pouringby blowing an argon (Ar) gas for 5 minutes with a degassing device.

In the case of strontium, an aluminum master alloy including strontiumwas added and specimens were manufactured by tapping after maintainingfor a predetermined time.

Specimens used for mechanical property measurement in each ExperimentalExample were manufactured by using die casting. Specifically, rod-shapedtensile test specimens were cast by using a TOYO die casting machinehaving a mold clamping force of 1300 KN, and tensile tests were thenperformed two days later after the specimens were cast in order toreduce deviations in mechanical properties. Seven or more specimens wereused for measuring mechanical property and an average value thereof waspresented as a result.

Die casting used in the present test was performed under conditions thata casting temperature ranges from 963 to 987 K and a die temperatureranges 463 to 473 K. The specimens used in the tests were prepared asNo. 14 rod-shaped proportional specimens according to the KSB0802standard.

Also, samples were collected from a center portion of the tensile testspecimens for microstructural observations by using an opticalmicroscope. The collected samples were polished by using polishingpapers and clothes, then cleaned with alcohol for 20 minutes, andthereafter etched. Also, analyses using a scanning electron microscope(SEM) and an energy dispersive spectrometer (EDS) were performed inorder to analyze the solubility of zinc in the α-aluminum phase matrixand the types and shapes of the eutectic phase formed.

Meanwhile, a commercial aluminum ADC12 alloy was used as a subject forcomparing tensile strengths of the aluminum alloys according toExperimental Examples, and FIG. 1 shows tensile test results of alloysprepared by Experimental Example 19 and the ADC12 alloy.

Referring to Table 1, when comparing Example 21 and Comparative Example1 having the same copper and zinc compositions, the tensile strength ofExample 21 with silicon added was increased 110 MPa in comparison withComparative Example 1 with no silicon added. Therefore, it can beunderstood that values of tensile strength are considerably improvedaccording to the addition of silicon in the case of the aluminum alloyaccording to an embodiment of the present invention.

Also, referring to FIG. 1, it can also be understood that excellentresults are obtained, in which the tensile strengths of the alloysaccording to the present Experimental Examples 19 is 120 MPa or morehigher than the tensile strength of the ADC12 alloy which is acommercial aluminum alloy having zinc and copper as major alloyingelements.

Therefore, it can be understood that the aluminum alloys according to anembodiment of the present invention exhibit very good mechanicalstrength characteristics in comparison with a typical commercialaluminum alloy.

The reason why the aluminum alloys according to the present ExperimentalExamples exhibit better properties than the ADC12 alloy is consideredthat alloy structures are refined by adding silicon together with zincand copper to aluminum.

Hereinafter, for the simplicity of the description, Al-xZn-ySi-zCudenotes an aluminum alloy, where x, y, and z are weight percents ofzinc, silicon, and copper added to aluminum, respectively.

FIGS. 2( a), 2(b) and 2(c) show SEM observation results obtained fromthe alloy structures of Al-30Zn, Al-30Zn-6Si-2Cu and Al-40Zn-6Si-2Cualloys, respectively.

Referring to FIG. 2( a), in the case of the Al-30Zn alloy, it can beunderstood that an Al—Zn eutectic phase is uniformly distributed ingrain boundaries due to the surplus zinc which is not dissolved in theprimary α-phase.

In contrast, referring to FIG. 2( b), it can be understood that thegrain size in the Al-30Zn-6Si-2Cu alloy is considerably decreased to arange of about few μm to 20 μm because the growth of the primary α-phaseis prevented.

FIG. 3 shows EDS analysis results of zinc contents (wt %) in eachregions of the Al-30Zn-6Si-2Cu alloy shown in FIG. 2( b) together with atable.

As shown in FIG. 3, it can be understood that zinc is dissolved up to 18wt % in a α-Al phase (Region 1) and zinc also stably exists up to 18 wt% around a eutectic Si-phase (Region 2). At this time, it is consideredthat the surplus zinc undissolved reacts with aluminum and copper toform Al—Zn—Cu compounds (Regions 3 and 4). It is estimated that theAl—Zn—Cu compounds contribute to the refinement of grains by preventingthe movement of the grains. Therefore, it is considered that thecrystallization of the Al—Cu—Zn compounds as well as the eutecticSi-phase may contribute to improving the strength of the aluminum alloy.

However, as shown in FIG. 2( c), the eutectic Si-phase is notdistributed at grain boundaries but exists in the primary α-phase. As aresult, the size of the grains increases so that a decrease in thestrength is expected. Therefore, in terms of strength improvement, it isestimated that the zinc content may be adjusted to less than 40 wt %.

Experimental results according to the alloy compositions presented inTable 1 will be described in more detail below.

Referring to Table 1, Experimental Examples 5, 6, 14, 15, 16 and 17, inwhich the silicon content is in a range of more than 6 wt % to 8 wt % orless and the copper content is in a range of 2 to 3.5 wt %, showedrelatively excellent tensile strengths in a range of 430 to 445 MPa forall zinc contents.

Therefore, it is considered that the aluminum alloys according to anembodiment of the present invention show relatively excellent and stablestrength characteristics when the silicon content is more than 6 wt % incomparison with when the silicon content is 6 wt % or less. All ofExperimental Examples 19 to 21 correspond to aluminum alloys in whichstrontium is further added to 0.02 to 0.1 wt % as an additive element ofthe aluminum alloy in addition to silicon, copper, and zinc. WhenExperimental Examples 19 and 20 are compared with Experimental Examples18 and 2, tensile strengths are increased in a range of 20 to 60 MPa ormore. It is considered that the considerable increases in the tensilestrengths are due to the refinement of the eutectic Si-phase accordingto the addition of strontium.

FIGS. 4( a) and 4(b) show SEM observation results obtained from thealloy structures of Experimental Example 18 with no strontium added andan aluminum alloy which has the same silicon, copper and zinccompositions as Experimental Example 18 with 0.04 wt % of strontiumfurther added.

When comparing between the microstructures (see arrows) of the eutecticSi-phases in FIGS. 4( a) and 4(b), it can be confirmed that the finereutectic Si-phase is obtained when strontium is added.

Meanwhile, when comparing Experimental Examples 19 and 21, a relativelybetter tensile strength was obtained when the strontium content is 0.02wt % in comparison with when the strontium content is 0.1 wt %.Therefore, it can be understood that the strontium content needs to bemaintained less than 0.1 wt %.

Aluminum alloys and aluminum alloy castings according to the embodimentsof the present invention have excellent strengths in comparison withtypical commercial aluminum alloys, and also exhibit extremelylightweight characteristics in comparison with stainless steels.Therefore, the aluminum alloys and aluminum alloy castings according tothe embodiments of the present invention can be stably applied tocompact and lightweight products as well as large products.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An aluminum alloy comprising: 4 wt % to 13 wt %of silicon (Si); 1 wt % to 5 wt % of copper (Cu); 26 wt % or more andless than about 40 wt % of zinc (Zn); and a balance being aluminum (Al)and unavoidable impurities.
 2. The aluminum alloy of claim 1, wherein acontent of the silicon (Si) is 5 wt % to 10 wt %.
 3. The aluminum alloyof claim 2, wherein the content of the silicon (Si) is 5 wt % to 8 wt %or less.
 4. The aluminum alloy of claim 3, wherein a content of thecopper (Cu) is 2 wt % to 5 wt %.
 5. The aluminum alloy of claim 4,wherein a content of the zinc (Zn) is 26 wt % to 35 wt %.
 6. An aluminumalloy comprising: 4 wt % to 13 wt % of silicon (Si); 1 wt % to 5 wt % ofcopper (Cu); 26 wt % or more and less than 40 wt % of zinc (Zn); 0.1 wt% or less of strontium (Sr); and 43 wt % to t 69 wt % of aluminum (Al).7. The aluminum alloy of claim 6, wherein a content of the silicon (Si)is 5 wt % to 10 wt %.
 8. The aluminum alloy of claim 7, wherein thecontent of the silicon (Si) is 5 wt % to 8 wt % or less.
 9. The aluminumalloy of claim 8, wherein a content of the copper (Cu) is 2 wt % to 5 wt%.
 10. The aluminum alloy of claim 9, wherein a content of the zinc (Zn)is 26 wt % to 35 wt %.
 11. The aluminum alloy of claim 6, wherein acontent of the strontium (Sr) is 0.04 wt % or less (excluding 0). 12.The aluminum alloy of claim 11, wherein the content of the strontium(Sr) is 0.02 wt % or less (excluding 0).
 13. The aluminum alloy of claim6, further comprising a total of about 3 wt % or less (more than 0) ofany one or more elements selected from the group consisting of titanium(Ti), magnesium (Mg), nickel (Ni), vanadium (V), tin (Sn), iron (Fe),chromium (Cr), zirconium (Zr), scandium (Sc), and manganese (Mn).
 14. Analuminum alloy casting manufactured by using the aluminum alloyaccording to any one of claims 1 to 13.